Enameling composition and the like and method of making the same



Patented Aug. 1 0, 1943 UNETED STATES PATEN 7 nNAMELmGcomosmoN AND THE LIKE.

. AND arnon or MAKING 'rrm SAME Leon J. Frost and Charles H. Commons, Jr.,

Niagara FallsuN. Y., asslg'nors to The Titan! Alloy Manufacturing Company, New York, N. Y a. corporation of Maine V Ni. Drawing. Application August 31,1939, ,4 senainazaam -8Claims.

This application is a continuation-in-part of,

copending application Serial No; February 24, 1937. a

.Thlsinvention relates to vitreous enamels and the like of high opacity and relatively white in color, and to the method of producing the same.-

(Cl. roe-4 8) coating.

- to the ware, while the metal 'base imparts strength to the hard'butrsomewhat brittle glass L It is thus seen that-an opacifier is included in the raw frit batch, and in addition more opacifier may be added "at the mill. As the opacifier More particularly, it relates to such enamels and l the like containing zirconium compounds as opacifiers.

--Inthe manufacture of enamels for application to metal bases, and to asomewhat lesser extent monate) have been extensively used. Both these 'materials are relatively insoluble in thefglass in such enamels, either tin oxide or antimony oxide (or its compounds, such as sodium antimelt, opacity thus resulting from diffuse reflecto ceramic bases, the customary procedure is to mix predetermined amountsof various materials into a fairly homogeneous mass and charge this batch into a preheated smelter. Heat is applied until the'reactions'have proceeded to a point tion of incident light from the suspended particles of opacifier. Both material's, however, suffer from thedisadvantage that they are readily reducible to dark-colored materials (sub-oxide or Qmetal) which in most cases are undesirable. -In

where the mass becomes asmooth liquid which is process enameling is used on heavy cast iron articles which hold considerable heat. For" this process the frit is'milled dry with not morethan about 3% opacifier until the material is fine enough to be easily shaken through a sieve onto the hot ware where it fuses onto the metal, due to the retained heat of the latter.

The more general process,,which is necessary for lighter weight ware, is known as the wet process. In thisprocess the frlt, together with water, clay, opacifier, color and electrolyte (if any) are charged into a mill and ground to suitable fineness for satisfactory handling and application. The slip thus formed is either sprayed onto the ware or the were dipped into the slip and the excess enamel eitherdrained or shaken off.- The ware is allowed to dry by evaporation of the water and is then put into a suitable furnace and fired for a time and at a temperature necessary to melt the glass and have it adhere firmly to the ware. Usually, a colored ground coat is first employed to promote adhesion and to prevent the reduction of the opacifier (or other constituents) in the enamel by the metallic base. After firing the ground coat, the process is repeated with the cover coat. One, two or even three cover coats maybe applied depending on the properties of the enamel, etc. When finished, the enamel imparts color, hardness and surface addition, antimony oxide, though less expensive than tin oxide, is quite poisonous. To overcome these disadvantages, zirconium oxide has been suggested as an opacifier. However, becauseof its relatively high solubility in the glass, so much of it was necessary that its costwas' equal to or greater than that of antimony oxide when used in the frlt. .It found'considerable usefulness as a mill addition opacifier because in the short firing time of the enamel on the ware (two to five minutes compared to one to threehours in the smelter) not very much or the zirconium oxide had time -to-go into solution in the glass and thus satisfactory and economical results were obtained. It was therefore afuseiul mill addition opacifier for usewith frits containing variable amounts of tin oxide or antimony oxide opacifier.

Attempts have also been made to employ zirconium oxide as a frlt opacifier. Mere loading of the frlt with zirconium oxide is objectionable not only because of the increased cost, but also because the refractoriness of the zirconium oxide increases the difiicultyof handling. Other compositions have been suggested in order to produce high opacity in the frit, as exemplified by vduce such enamels having good gloss and chemical and mechanical durability. It is another object to provide methods of forming enameling compositions which can form highly opaque enamel coatings with relatively thin coatings. f

It has now been found that, under certain conditions, high opacity in the frit is neither necessary nor desirable. If a frit is made with zirconium compounds in a suitable frit compositions, such compounds may, in accordance with the present invention, go into solution in the melt. By adding a seeding agent, such as a zirconium compound, at'the mill, the

zirconium compound in the frit can be made to reprecipitate in the enameling operation to form a densely opaque enamel. The frits produced by this method are ,so translucent and lack so much opacity, when considered in the-light of present practice, that they would normally have been discarded as worthless without expending the effort of trying them as enamels. However, when properly compounded and suitably seeded they have been found to produce very densely opaque enamels on the ware. The results of the work along this line have produced enamels of such outstanding merit that it is believed they meet the requirements of the enameling and glazing industry for which a solution has long been sought.

In order to secure, in accordance with this invention, a highly opaque enamel from a frit which is relatively translucent, the composition of the frit should be kept within certain limits. The important ingredients of the frit are alumimun, zirconium and fluorine, present in the composition in the form of compounds of these elements. The quantity of zirconium should be 1% to 9%, and preferably 5% to 9%. Similarly, the amount of aluminum should exceed 5%, and for best results should lie between 6% and 10%. When it is present in lesser quantities than this it becomes very dimcult or impossible to secure good opacity from relatively transparent frits, without abnormally high mill opacifier additions. The quantity of fluorine should be 3.5% to and preferably 7% to 14%.

The zirconium compound utilized in this connection is preferably zircon, since this occurs naturally in a relatively pure form and needs no chemical transformation to prepare it for use. Other zirconium compounds, however, may also be used, particularly those which do not undergo chemical change when subjected to the they produce, but in general the quantities should he kept below the following maxima:

FezOa Below 0.08 MnOa Below 0.03 CrzOa Below 0.005 V205 "Below 0.005 CuO "Below-0.01 NiiO:- Below 0.01

ever, is only harmful when it is dmired to pro- 'duce an opaque enamel of a high degree of whiteness. When producing colored enamels, in fact, it may even be desired to add the oxidm of one or more of these otherwise undesirable ele- .ments. The invention also contemplates. the

manufacture of colored enamels in addition to white enamels.

Where whiteness is desired, however, the aluminum compound'should berelatively free from the above impurities. Any suitable chemically purified material, such as alumina hydrate, can

beused. It is preferred, however, to use certain naturally occurring aluminum containing minerals which are available in a sufficient state of purity for this use. By far the best ofsuch minerals is pyrophyllite, which is cheap, easily available and veryv pure. Other materials, however. can also be used. Among these are naturally occurring sillimanite or andalusite, partially purified by leaching with dilute hydmchloric acid, a highly purified grade of English china clay, and topaz, bauxite or kyanite, if available in a sufllciently pure state. Suitable samples of these naturally occurring materials show percentages of undesirable impurities as shown in Table I.

TABLE I Sillimanite Andalusite English P5 mphynlte acid leached acid leached china clay 0. 012 0. 20 0. 6 0. 20 Trace 0. 005 Trace 0. 01 None None 0. 00l Trace Trace Trace 0. 0i 0. 005 0. 01 0. Trace 0. 005 0. 005 0. 2 0. 8 0. 9 0. 05

As mentioned above, however, pyrophyllite is the preferred material. Not only is it cheaper, but it produces better results. The mineral pyrophyllite is soft and resembles talc in appearance.

high temperatures employed in baking or firing the enamels.

Among such compounds are zir-' conium oxide, calcium zirconium silicate, sodium 2 zirconium silicate, zinc zirconiumzsilicate, 'and others. It is necessary onlyithat such zirconium compounds do not contain any appre ciable' quantities of the elements whichare harm? 7 It has been found that the occurrence of certain elements in the present type of frit produces The undesirable impurities undesirable results. are iron, chromium, copper, manganese, vanadium, nickel and, to a lesser extent,ftitanium.

These elements vary in the harmful effect which It has the mineralogical composition of approxi mately Al2Oa.4SiO2.H2O, and is optically negative with B'axis' perpendicular to the nearly perfect basal cleavage plane. a

The fluorine" compound can be in the form of naturally occurring. materials, such as cryoli-te or fluorspar, or synthetic materials such as sodium fluosilicate.

In addition to zirconium compounds, aluminum compounds and fluorine compounds, it is desirable to incorporatein the Hit certain other materials. Boron, 1n the form of boricoxide or borax is; -desirable.- .Silicon usually present in-the form of the silicates of zirconium and aiuminum, but it maybe desired to add further silicon in the form of quartz. 5 Other desired materials are calcium' (added, for example, in the form of limestone orfluorspar) sodium (added,

for example, in the form of sodium nitrate 0r. cryolite) and sometimes zinc oxide. In place of the sodium, other alkali metals, such as lithium or potassium may be used, Barium or strontium compounds may partially, replace the'calcium customary fashion.

2,326,848 compounds. Except for aluminum, zirconium and fluorine, these compounds are in general incorporated in the frit for purposes other than securing opacity in the final enamel. The preferred quantities of these materialsare as'follows: sodium (or other alkali metal) 11% to 16% I (more preferably 7% to 13%); boron. 1% to 8% (more preferably 3% to 7%), silicon 8% to 26% (more preferably 12% M2296), and calcium -1%' n The physical form of the various'ingredients is not a necessary feature vof this invention.

to 15% (more preferably 2% to 9%) However, is is preferred that they be in a relatively finely divided form, in order that the smelting time may be as low as possible. This is particularly true'of the more refractory ingredients.

For example, it is preferred to use finely milled zircon rather than granular zircon, although the latter can also be used.

After the raw frit batch is com-pounded it is smelted at a relatively high temperature, such as in the. neighborhood of 2000" F. As distinct from prior frits containing zirconium compounds as an opacifler, it is not necessary that the smelting temperature be so accurately controlled. The reason for this is that securing opacity in the frit isneither desirable nor undesirable. However, 'there must be sufficient control tc'avoid loss or destruction of enamel constituents.

After the frit is formed it is quenched in the g It is then milled with a minor quantity of a zirconium compound opacifier, such as zirconium-oxide, forexample 3 to 10 parts of zirconium oxide per .100 parts of frit or other suitable seeding agent, tog'ether with other desired constituents such as clay, magnesium with the Bausch and Lornbv instrument. The Hunter readings will be generally about 4 to 4% points lower, depending on the exact specular reflectibhof the particular samplebeingimeasur'ed.

This batch was mixed and then smelted at ,a

temperature of 1900 F. to form a melt, which was then pouredinto water and quenched. 100

parts of this frit was milled with. 6 parts of clay,

-6 parts of zirconium oxide, 0.25 part of magnesium'carbonateandabout 40 parts'of water to a fineness of plus 200 mesh. "The slip'thusformed was applied'byspraying to sheetiron, previously supplied with' a ground coat, at the rate of 72 carbonate or sodium nitrite, and'water tosecure properconsistency. It is then applied' to the finished article and fired at an elevated tem pera-ture in well-known fashion. Surprisingly enough, the resulting enamel exhibits high opacity, evidently due to the fact that the opacifier added at the mill seeds out or precipitates the opacifler incorporated in the frit;

Having described'the invention, the following examples are now given. The compositions given in these examples show the types of frit compositions-which have been tried and foundvaluable for this purpose. In some cases the types represent the extremes in compositions while others are the preferred compositions found to be the most practical. In each case the ingredients may consist of various combinations of compounds so as to give the desired final compositions. Where the minerals pyrophyllite, sillimanite, andal-usite or English china clay are specified in the exam-pies, it is understood that specimens approximating the compositions shown in Table I were used.

In the enameling art two or more types of instruments are used to evaluate the quantity of light reflected from an enameled surface, and to more accurately judge opacity than was possible by eye alone. The Hunter instrument is so constructed that it separates diffuse reflection and specular reflection and evaluates them separately. This is advantageous for research work, as the diffuse reflection is the real basis for white opacity or hiding power. However, the Bausch and Lomb instrument integrates the diffuse reflection plus a component of specular reflection and produces a higher reading, but one which is more in line with what the human eye sees under grams per sq. ft. total for two coats. After firing at 1500 F; for 2 to 4 minutes, the surface is highly lustrous andof a good white and shows a reflectance of 37.

A frit was prepared: as. in Example'll from the following ingredients (parts by weight):

Ihgredientsofraw batchXpdrtsbg/ weighti t Pyrophyllite 1 36.02 I Aluminumhydrate- -L. 4.53 Milled zircon 12.31 limeston 8.84 Anhydrous borax-.. a "24.57- Soda nitre 3.50 Cry A 14.00 Fluorspar 5.00 Zinc oxi 5.00

Raw total 113.77 ,A slip was formed from this frit as in. Example 1 andfired as in Example reflectance of 87. v 1 Thisbatch required about 30% less time to smelt and produced an enamel of better working properties than Examplel.

EXAMPLE 3 .1. The surface shows a e To show the effect of decreasing the zirconium contentto too great an extent, the following example was prepared. A frit was prepared as in Example '1 from the following ingredients (parts by weight) Ingredients of raw batch (parts by weight) Pyrophyllite 48.35 Quartz 2.01 Milled zircon 1.54 Limestone 8.84 Anhydrous borax 24.57 Sodium nitrate 3.50 Cryolite 14.00 Fluorspar 5.00 Zincxi 5.00

Zinc oxide reflectance of 73%.

EXAMPIES 4-11 The following examples were prepared by mixing the raw ingredients as shown by Table 11, below, and smelting at a temperature of 2000' to 2100 F. until a melt forming smooth strings results.

TABLE II Parts by weiqht Dehydrated borax Sodium fluosilicate Fluorspar-.- Zinc oxide girconif 11.1%....

W 1 3 Aluminum hydrate Zinc zirconium silicate Special opacifler l Quartz powder Boric acid Zirconium spinel. Silllmanite Andalusitenu English china clay Dehydrated borax Sodium fiuosilicate Fluors QHOIPQOO yl Aluminum hydrate Zinc zirconium silicate Special opacifier 1 164. 6 Zirconium oxide Zirconium spinelm.

This product is a zirconium opacifler produced in accordance with U. 8. Patent No. 1,789,311.

100 parts'oi each of these irits were each milled A slip was formed from this irlt as in Example 1 and fired as in Example 1. The surface shows a Tana: IV

Examples Per cent Per cent Per cent Although the above description and examples deal with the compounding oi irits for enameling on metal bases, the present enameling compositions arealso suitable for glazing ceramic bodies with equally promising results. 'Ithas also been found that similar compositions, with appropriate modifications, can be made up as glasses of various shapes, such asjars, table ware, sheets,

with 6 parts of enamelers clay, 6 parts of zirconium oxide, 0.1 part of NaNO:, and 38parts of water to a fineness 01 +200 mesh. The slip thus 'formed was applied by spraying to sheet iron,

previously supplied wlth'a ground coat, .at-the rate of 72 grams per sq. ft. for two coats. Alter firing at 1500 F. for 2% to4minutes, the surfaces are highly'lustrous and of afgood creamwhite in color, and show refiectances as follows:

TABLE III- Examples 4 v15. 0 7 s e Reflectance 84.0 87.1 84.0 an 84.7 80.0 84.5 83.9

The irits in the above examples showed calculated percentage compositions, exclusive of impurities, according to the following table:

be varied to secure characteristics desired for these uses.

There are, also, other additions which may be added by skilled operators to produce certain specific eflects well known in the art which are not concerned with the opacity derived from zirconium and should be considered as within the scope of this invention. Thus antimony might be added in small amounts to improve the acid resistance, color oxides may be added to obtain various color effects, strontium compounds to improve brilliance and workability, etc.

As many variations are possible within the scope of this invention, it is not intended to-be limited except as defined by the appended claims.

' We claim: 1. A composition capable,.upon smelting, of forming a. relatively translucent frit, in turn capable of producing highly opaque enamels and the like, comprising a mixture of compounds contaming approximately the following content by 4 analysis: sodium about 11%; calcium about.6%;

boron about 5%: alumlnumjabout 8%; silicon about l3%'; zirconium about 7% zinc about 4%; 7

oxygen about-37 and fluorine about 9%.

2. A composition capable, upon smelting, of

. forming a relatively translucent 'i'rit. in turn capable of producing highly opaque enamels and the like, comprising a mixture of compounds containing approximately the following content by analysis: sodium about 10.69%; calcium about 5.85%; boron about 5.06%; aluminum about I like. comprising a mixture of compounds con.-.

77.61%; silicon about'13.36%: zirconium about 6.98%; zinc about 3.85%; oxygen and fluorine 9.42%. I

3. A composition capable, upon smelting, of forming a relativelytranslucent irit, in turn capable of producing highly opaque enamels and the about 37.18%;

talning approximately the following ingredients substantially in parts by -weight, vizzzirconium oxide 8.00; quartz powder 30.42; dehydrated borax 28.91; sodium nitrate 3.23; fluorspar 5.00; limestone 7.68; cryolite 12.00; and aluminum hydrate 21.53.

4. A composition capable, upon smelting, of forming a relatively translucent frit, in turn capable of producing highly opaque enamels and the like, comprising a mixture of compounds containing approximately the following ingredients substantially in parts by weight, viz: pyrophyllite 36.02; aluminum hydrate 4.53; milled zirconium silicate (zircon) 12.31; limestone 8.84; anhydrous borax 24.57; sodium nitrate 3.50; cryolite 14.00; fiuorspar 5.00 and zinc oxide 5.00.

5. A composition capable, upon smelting, of forming a relatively translucent frit, in turn capable of producing highly opaque enamels and the like, comprising a mixture of compounds containing approximately the following ingredients substantially in parts by weight, viz: pyrophyllite 48.35; quartz 2.01; milled zirconium silicate (zircon) 1.54; limestone 8.84; anhydrous I forming a relatively translucent frit, in turn capable of producing highly opaque enamels and the like, comprising pyrophyllite, zirconium silicate, and a fluorine compound.

8. A composition capable, upon smelting, of

forming a relatively translucent frit, in turn capable of producing highly opaque enamels'and the like, comprising pyrophyllite, zirconium silicate, and a' fluorine compound, the amount of pyrophyllite being in excess of that of zirconium silicate.

LEON J. FROST. CHARLESH. COMMONS, JR. 

